Air actuated electrical switch



June 1, 1965 E. KOCK 3,187,134

AIR ACTUATED ELECTRICAL SWITCH Filed March 22, 1961 III IN V EN TOR.

ERHARD OCK F/g 2 BY Z M zit/c ings United States Patent Ofitice 3,187,134 Patented June 1, 1965 3,187,134 AIR ACTUATED ELECTRICAL SWITCH Erhard Kocir, Indianapolis, Ind., assignor to Ransburg Electro-Coating Corp., Indianapolis, Ind., a corporation of Indiana Filed Mar. 22, 1961, Ser. No. 97,599 2 Claims. (Cl. 200-81.9)

This invention relates to an electrical apparatus, and more particularly to an electrical switch actuated by changes in air flow.

In certain types of electrostatic spray-coating systems, a spray gun is employed from which the coating material is discharged in the form of spray by means of air under pressure. A charging electrode is operatively associated with the spray being discharged from the gun to electrostatically charge said spray. It is thus apparent that the gun may be electrically tie-energized when it is not emitting a spray by controlling the voltage supplied to the charging electrode in conjunction with the air supplied to the gun.

It is thus an object of this invention to provide an air flow electrical switch which may be used in association with electrostatic spray equipment for controlling the voltage impressed upon such equipment, which may be easily and inexpensively manufactured from a relatively small number of parts, which will be sturdy and durable in use, and which will be sensitive to changes in air flow to effect switch actuation.

In accordance with the preferred form of the invention, there is provided a switch casing having an electrical switch mounted therein. Air inlet and air outlet ports are formed in said casing, and a piston is movably carried within the casing to define a restricted air flow passage between said ports, whereby a predetermined rate of air flow through said flow passage will move said piston into engagement with said switch to actuate the same.

Other objects and features of the invention will become apparent from the more detailed description which follows and from the accompanying drawings, in which:

FIG. 1 is an isometric, partially schematic view of an electrostatic spray-coating system used in association with a switch embodying my invention;

FIG. 2 is a vertical axial section through a switch embodying my invention; and

FIG. 3 is a top plan view of the switch shown in FIG. 2.

FIG. 1 shows my switch employed in association with an electrostatic spray-coating system comprising a spray gun 10, positioned to spray a series of articles 11, carried through a coating zone by a grounded conveyor 12. Coating material is supplied to the gun through a flexible hose 13 extending from a paint tank 14 maintained under pressure in a known manner to feed the coating material. The gun employs compressed air for atomizing the coating material, with such air being supplied to the gun through a flexible air conduit 15 and 15 from a source 16 under appropriate pressure. A high voltage for charging the spray issuing from the gun It) is conducted to the gun through a flexible cable 17 connected to one terminal of a high voltage source or power pack 18. To provide an on-off control for the voltage impressed upon the gun 10, the air flow electrical switch 20 comprising the subject matter of the instant application is interposed in the air conduit 15 and 15', with one terminal of said switch being connected to a conductor 21 leading to a source of electric power and the other terminal of said switch being connected to a conductor 22 leading to the power pack 18.

As shown in FIG. 2, the switch comprises a casing 24, conveniently in the form of a metal casting having a generally cylindrical side wall 25 closed at one of its ends by an end wall 26 integral with the side wall 25. The opposite end of the casing is closed by a removable end cap 27 received in an O-ring seal 40 and supported on a shoulder formed in the inner face of the side wall 25. The end cap 27 is retained in position on the casing by a snap ring 28 received in an annular recess formed in the inner face of the casing side wall 25. The casing thus defines an enclosed elongated air chamber 29 which is provided with an air inlet port 30 and an air outlet port 31 formed in the casing end and side walls, respectively. In the illustrated embodiment, the inlet port 30 is connected to the air conduit 15' by a nipple 32, and the outlet port 31 is connected to the air conduit 15 by a nipple 33.

Mounted on the side wall 25 adjacent one end of the chamber 29, as on a bracket 34, is an electrical switch 36 having an outwardly biased actuating contact button 37 and a pair of terminals 38 and 39 projecting outwardly through the end cap 27; the terminal 38 being adapted to be connected to a source of electrical power, as by the conductor 21, and the terminal 39 being adapted to be connected to the high voltage source 18, as by the conductor 22.

The inner face of the casing side wall 25 is shouldered adjacent the inlet port 30, as at 41, to support a piston 42 slidably carried in the air chamber 29. The piston 42 comprises a pair of parallel heads 44 and 45 interconnected by an elongated web 46. The diameters of the heads are slightly smaller than the diameter of the air chamber 29, but their extended axial spacing provided by the web 46 prevents the edges of said heads from bind ing against the chamber defining walls and the piston from becoming cocked.

As shown, the length of the web is such that when the switch is open or closed the head 45 is interposed between the inlet and outlet ports 30 and 31, and the head 44 is positioned between the switch 36 and outlet port 31 to dispose the outlet port 31 in open communication with the air chamber 29. The head 45 thus resists the flow of air through the chamber 29, with the spacing between its periphery and the Walls of the chamber and the biasing force on the button 37 determining the rate of air flow through the chamber necessary to move the piston 42 into position to engage and actuate the switch contact button 37 for closing the switch 36. For example, if the radial spacing between the head 45 and the walls of the chamber 29 is in the order of about 7 mils and the outwardly biasing force on the contact button 37 is 4 ounces, air entering the chamber at a rate of flow associated with an atomizing air pressure measured at the gun of about 3 p.s.i. will be sufiicient to move the piston into engagement with the contact button 37 and overcome the biasing force on said button to cause it to close the switch 36. With the same outward biasing force on the contact button 37, a larger spacing between the head 45 and chamber walls will, of course, increase the rate of air flow necessary to effect piston movement; and conversely, a smaller spacing will decrease the rate of air flow necessary to effect such movement.

The face of the head 44 adjacent the switch 36 is conveniently covered with a resilient pad 48, so that when the piston has moved a sufiicient distance in the chamber to engage the contact button, the pad 48 will engage said button and cushion the force of the piston against it. As shown in FIG. 2, it is also desirable to locate the switch on the mounting bracket 34 to dispose the edge of said bracket adjacent the piston in the same plane as the face of the contact button when said button is in its switchclosed position, whereby said bracket tends to adsorb the impact forces of the piston against the button which might result from high rates of air flow through the chamber 29.

As long as the air flowing through the chamber 29 is suflicient to move the piston into a position to actuate the button 37, the button will remain depressed to close the switch 36, and the high voltage source 18 will impress a high voltage on the gun It to electrostatically charge the spray discharged therefrom. But should the air flow drop to a level sufiiciently lower than that required to overcome the biasing action of the button, the button will force said piston toward a seated position on the shoulder 41 and the switch will open.

I claim:

1. In an air flow actuated electrical apparatus, a casing having a unitary chamber of substantially uniform crosssection throughout at least the length of the chamber through which a switch-actuating piston moves and provided with an air inlet port and an air outlet port in axially spaced relationship, an electrical switch mounted in said chamber and having an outwardly biased, actuating contact button, and said piston being carried wholly Within said chamber and freely slidable therein, said piston having a plurality of heads interconnected by an elongated web having a cross-section substantially smaller than least one of said heads retained between said inlet and 7 outlet ports in circumferentially closely spaced relation said heads and axially spacing the heads to prevent the edges of the heads from binding against the chamber walls and the piston from becoming cocked in said chamber, at

to the chamber walls to cause at least one of said heads to restrict the tree flow of air from said inlet port to said outlet port and to cause said piston to move into actuating engagement with said contact button to actuate said switch upon a predetermined air flow through said chamher.

2. The invention as set forth in claim 1 in which'said chamber has a shoulder formed therein adjacent said inlet port against which said at least one head is seatable.

References Cited by the Examiner UNITED STATES PATENTS 1,961,004 5/34 Lemaitre et al 20082 2,096,492 10/ 37 Hewitt 20082 2,244,007 6/41 Harrington et a1. 20082 2,618,965 11/52 Gray 200-82 2,916,576 12/59 Croskey et al. 20081.9 3,026,387 3/62 Ashbaugh 200-82 BERNARD A. GILHEANY, Primary Examiner.

MAX L. LEVY, ROBERT K. SCI-IAEFER, Examiners. 

1. IN AN AIR FLOW ACTUATED ELECTRICAL APPARATUS, A CASING HAVING A UNITARY CHAMBER OF SUBSTANTIALLY UNIFORM CROSSSECTION THROUGHOUT AT LEAST THE LENGTH OF THE CHAMBER THROUGH WHICH A SWITCH-ACTUATING PISTON MOVES AND PROVIDED WITH AN AIR INLET PORT AND AN AIR OUTLET PORT IN AXIALLY SPACED RELATIONSHIP, AN ELECTRICAL SWITCH MOUNTED IN SAID CHAMBER AND HAVING AN OUTWARDLY BIASED, ACTUATING CONTACT BUTTON, AND SAID PISTON BEING CARRIED WHOLLY WITHIN SAID CHAMBER AND FREELY SLIDABLE THEREIN, SAID PISTON HAVING A PLURALITY OF HEADS INTERCONNECTED BY AN ELONGATED WEB HAVING A CROSS-SECTION SUBSTANTIALLY SMALLER THAN SAID HEADS AND AXIALLY SPACING THE HEADS TO PREVENT THE EDGES OF THE HEADS FROM BINDING AGAINST THE CHAMBER WALLS AND THE PISTON FROM BECOMING COCKED IN SAID CHAMBER, AT LEAST ONE OF SAID HEADS RETAINED BETWEEN SAID INLET AND OUTLET PORTS IN CIRCUMFERENTIALLY CLOSELY SPACED RELATION TO THE CHAMBER WALLS TO CAUSE AT LEAST ONE OF SAID HEADS TO RESTRICT THE FREE FLOW OF AIR FROM SAID INLET PORT TO SAID OUTLET PORT AND TO CAUSE SAID PISTON TO MOVE INTO ACTUATING ENGAGEMENT WITH SAID CONTACT BUTTON TO ACTUATE SAID SWITCH UPON A PREDETERMINED AIR FLOW THROUGH SAID CHAMBER. 